The present invention relates to a charging device for used in a charger which charges a body such as a photosensitive body, transfer charger, discharger, or the like, and an electrophotographic apparatus such as a copying machine, printer, or facsimile.
Charging devices each for use in an image formation apparatus include a corona charging device, a roller charging device, a brush charging device, and a solid charging device. The corona charging device is the most popular one. The corona charging device has, however, a drawback such that it generates a very large amount of ozone. As a counter measure for this drawback, for example, Japanese laid open No. (hereafter referred to as JP-A) 9-114192 discloses a unit which reduces the ozone generating amount. In this unit, a discharge is performed by using a very thin wire of 40 to 50 microns, thereby reducing more than the half of the ozone generating amount.
JP-A-6-324556 discloses a unit in which a metal casing is arranged on three sides of a wire, a metal mesh electrode is arranged near the open side, and ozone generated from the wire is made remain to increase the probability of collision of ozone molecules, thereby reducing the amount of ozone released.
A roller charging device is disclosed in JP-A-56-91253 and is being actively examined in recent years. A brush charging device is disclosed in JP-A-55-29837 and so on. A solid charging device is disclosed in JP-A-54-53537.
JP-A-5-94077 discloses a device in which a number of discharge electrodes are arranged on an insulating member at very small intervals. JP-A-6-75457 discloses a technique where a distance between a charging device and a member on which recording is performed is set to a range of 500 to 3000 xcexcm so that ion flying distance can be shorten, thereby suppressing diffusion of ozone and to preventing adhesion of toner and the like.
JP-A-9-244350 discloses a discharging device comprising: a discharge electrode on a plate-shaped substrate; a creeping glow discharge unit arranged around the discharge electrode, and a cover which covers the whole discharging device. JPA-9-115646 discloses a method of reducing NOx by using a material of a specific work function as the material of an electrode of a plane solid discharging device.
JP-A-8-315958 discloses a solid discharging device in which a discharge electrode and a counter electrode which extend in parallel to each other on an insulating substrate are formed, a sharp edge-shaped electric field concentration part is formed at the periphery on the side facing the counter electrode of the discharge electrode, and the side facing the discharge electrode of the counter electrode is covered with an insulating film.
JP-A-11-95526 discloses a charging device in which a plurality of discharging units each can independently discharge are formed on a common substrate. Each of the discharging units comprises: a discharge electrode arranged facing a member to be charged which moves relatively, for generating charges applied to the member to be charged; and an ionization range control electrode which is arranged between the member to be charged and the discharge electrode and controls an ionization area of a discharge in an electric field between the charged member and the discharge electrode so as to be between the discharge electrode and the ionization range control electrode.
There is an ozone adsorbent for use in a charging device, which oxidizes generated ozone by a catalyst function such an activated carbon and another ozone absorbent adsorbs ozone on its surface. The social trend in recent years is that the environmental conscious has been being improved. Standards for regulating the generation amount of ozone, such as UL standard, TUV standard, and BAM standard, are set for an image formation apparatus of an electrophotographic system by a plurality of groups many countries and regions.
The corona charging device generates a very large amount of ozone.
In the techniques disclosed in JP-A-9-114192 and JPA-6-324556, the amount of ozone of at most about 50% can be reduced and it is necessary to use an ozone adsorbent or the like.
In the roller charging device, the generation of ozone can be suppressed very much. The device is consequently regarded as a promising one, but the charges on the charged body tend to be uneven. Moreover, toner contamination on the roller surface and vibration due to an AC bias to be applied occurs, and moire or the like often occurs in an image. Further, since it is a rotary member and the roller surface has to be cleaned, the number of members is large. Besides, there are inconveniences such as dielectric breakdown in a photosensitive layer of a photosensitive body as a body to be charged, which causes pin holes, vibration sound, track of a charging roller (plasticizer), permanent deformation of the roller, and the like.
In the brush charging device, stripe charging unevenness, environmental variation, low-temperature streamer discharge, white spot, photosensitive body wear, accumulation of a worn photosensitive body, coming off of a brush, melting of a brush due to abnormal discharge by a damage in the photosensitive member, and the like occur.
Since the ozone adsorber deteriorates with time, it is necessary to replace and maintain an ozone filter.
Although the solid charging device has advantages of its small size and the like, the discharge area is wide and discomfort substances such as ozone and NOx cannot be reduced as much as expected.
It is an object of the invention to provide a smaller charging device which can reduce ozone and NOx generated and diffused, uniformly charge the surface of a body to be charged, and does not produce a bad image caused by the charging device.
It is another object of the invention to provide a charging device and an electrophotographic apparatus capable of realizing reduced ozone and uniformly charging the body to be charged.
According to one aspect of the invention, at least a pair of linear electrodes is surrounded by walls and the substrate. Therefore, ozone generated and diffused and Nox can be reduced and the size of the device can be reduced.
Further, the longitudinal direction of each of the linear electrodes is in parallel with the axial direction of the charged body. Therefore, the larger amount of charges can be discharged.
Further, the longitudinal direction of each of the linear electrodes may be in parallel with the moving direction of the charged body. Therefore, the construction of an electrode can be also simplified.
Further, a plurality of pairs of the linear electrodes is arranged so that the longitudinal direction of each of the linear electrodes is oblique with respect to the moving direction of the charged body. Therefore, even when paper powders, toner particles and the like on the charged body are partially adhered to an electrode, charging by the electrode is helped by the neighboring electrode.
Further, the substrate may be arranged almost perpendicular to the charged body. Therefore, since the paper powders and toner particles on the charged body are not easily adhered, the charging can be stably controlled.
Further, the wall may be formed so as to extend in the direction except for the direction of the charged body of the line electrode. Therefore, a larger amount of ozone resides in the space sandwiched by the walls and decomposition of ozone is promoted.
Further, the pair of linear electrodes may be arranged so that their electrode faces are opposite to each other. Therefore, a larger amount of ozone resides in the space sandwiched and decomposition of ozone is promoted.
Further, the tips of the linear electrodes may have a saw-tooth shape. Therefore, by concentration of an electric line of force on the tips of the teeth of the electrodes, the efficiency of discharge increases so that charging is performed with a relatively low voltage.
According to another aspect of this invention, a first electrode forms on a first substrate, and a second electrode forms on a second substrate and faces the first electrode over an insulating wall. Discharge occurs by applying an AC voltage across the first and second electrodes. Therefore, generated ions and the like are captured in the space between the substrates and do not escape so that the density of ozone increases.
Further, a bias electrode arranged on the charged body side generates a bias electric field between the bias electrode and the charged body may be also provided. Therefore, the charging amount of the charged body can be arbitrarily controlled. Furthermore, the bias electrode may be integrally formed with the body of the charging device. Therefore, the electrode can efficiently ejects only charges of a necessary polarity among charges generated by the discharge toward the body to be charged.
According to still another aspect of this invention, in a charging device having a space as an ion generating area defined between dielectrics sandwiching electrodes, the neighboring electrodes partially have different shapes. Therefore, the area where the electric field intensity is high is formed, and discharge occurs with a low voltage.
According to still another aspect of this invention, in a charging device having a space as an ion generating part defined between dielectrics sandwiching electrodes, an electrode forms a predetermined angle with a face of each of the dielectrics sandwiching the electrode. Therefore, the area where the electric field intensity is high is formed, and discharge occurs with a low voltage.
Further, in the charging device according to still another aspects of this invention, electrodes which are bilaterally symmetrical may be lined. Therefore, the area where the electric field intensity is high is formed, and discharge occurs with a low voltage.
Further, electrodes of the same shape may be lined. Therefore, with the above structure, the area where the electric field intensity is high is formed, and discharge occurs with a low voltage.
Further, the central part in cross section of the electrode maybe recessed. Therefore, with the above structure, the area where the electric field intensity is high is formed, and discharge occurs with a low voltage.
Further, three or more electrodes may be lined. Therefore, the discharge area becomes wider.
According to still another aspect of this invention, in a charging device having a space as an ion generating area defined between dielectrics sandwiching electrodes, the neighboring electrodes have a step in an ion ejecting direction, three or more electrodes are lined, and an electrode sandwiched by electrodes via dielectrics is recessed in the ion ejecting direction from the electrodes on both sides. Therefore, the area where the electric field intensity is high is formed, and discharge occurs with a low voltage.
Further, neighboring electrodes may have a step in an ion ejecting direction, three or more electrodes may be lined, and an electrode sandwiched by electrodes via dielectrics may be recessed in the ion ejecting direction from the electrodes on both sides. Therefore, the area where the electric field intensity is high is formed, discharge occurs with a low voltage.
Further, neighboring symmetrical electrodes may be paired, each of the pair of electrodes may be sandwiched by dielectrics, and the pair of electrodes may be recessed in the ion ejecting direction from the electrodes on both sides. Therefore, the area where the electric field intensity is high is formed, discharge occurs with a low voltage.
Further, the electrodes on both sides may be closed to the pair of electrodes. Therefore, the area where the electric field intensity is high is formed, discharge occurs with a low voltage.
Further, two or more sets each having the dielectrics, the pair of electrodes, and the electrodes on both sides may be lined. Therefore, the discharge area becomes wider.
Further, a grid electrode may be provided between the ion generating area and the charged body. Therefore, the discharge potential can be certainly obtained.
According to still another aspect of this invention, an electrophotographic apparatus comprises one of the above charging devices. Therefore, an electrophotographic apparatus which produces a small amount of ozone exhaust can be realized without using and ozone filter.
Other objects and features of this invention will become apparent from the following description with reference to the accompanying drawings.